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Tests & Procedures : Lab Tests

Blood Smear

Does this test have other names?

What is this test?

This is a blood test to look at the number and shape of your red and white blood cells and platelets to see whether they are normal. A blood smear can also detect parasites in your blood.

Although it's more common to have your blood analyzed by computer, blood smears are still routinely done to rule out or identify certain diseases. Unlike the analysis done by machine, these findings come from a laboratory scientist or doctor specializing in blood or infectious diseases. These specialists look at the blood cells on a slide and evaluate them. Sometimes a blood smear provides unexpected results.

Why do I need this test?

You may need this test if you have unexplained anemia or jaundice, a condition that causes your skin and eyes to turn yellow. If you feel tired or dizzy all the time, your doctor may suspect a problem with your blood and order this test. Your doctor may order the test if you have persistent or recurring fever and have traveled to a developing country, or if you've had a history of exposure to ticks. In particular, you may receive the test if your doctor suspects you have a parasite that carries an infectious disease, such as malaria.

Doctors typically use a blood smear to confirm the diagnosis for certain diseases. If your child has bouts of severe, unexplained chest pain, for example, he or she might have sickle cell anemia, an inherited disease that can be identified through a blood smear.

Your doctor may also order this test to monitor your blood cell count if you have gone through chemotherapy. This test may help him or her evaluate whether the treatment is working.

What other tests might I have along with this test?

Your doctor may also order a complete blood count, or CBC, which looks at the size and number of platelets and red and white blood cells. Another test commonly ordered with a blood smear is a reticulocyte count, which involves staining and counting the premature red blood cells that have left the bone marrow early.

Your doctor may also order a bone marrow biopsy, a test that looks at the blood cells inside your bone marrow, the spongy substance that makes blood cells in your bones. In this test, the doctor collects a tiny amount of bone marrow through a needle.

Finally, your doctor may order a chemistry panel or blood chemistry test, which measures substances such as electrolytes, sugar, and protein.

What do my test results mean?

Your test results will be either normal or abnormal. Your doctor will interpret that result based on your symptoms, the diagnosis he or she suspects, or the treatment you are undergoing. A blood smear can be used to help diagnose or monitor many conditions. Some of these include anemia, jaundice, sickle cell disease, thrombocytopenia, malaria, sudden kidney failure, G6PD deficiency, and certain cancers.

The results of a blood smear might include the number, size, and shape of your red blood cells. The results also might tell your doctor the number and type of your white blood cells, the number of platelets, or even whether you have a parasite.

The accuracy of the results depends on the skill and experience of the person reading the test. Talk with your doctor about the results.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Ask your doctor whether you can eat or drink immediately before giving blood.

How do I get ready for this test?

You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.